Randomized control trial of topical clonidine for treatment of painful diabetic neuropathy
A length-dependent neuropathy with pain in the feet is a common complication of diabetes (painful diabetic neuropathy, PDN). It was hypothesized that pain may arise from sensitizedhyperactive cutaneous nociceptors, and that this abnormal signaling may be reduced by topical administration of the α 2 -adrenergic agonist, clonidine, to the painful area. This was a randomized, double-blind, placebo-controlled, parallel-group, multi-center trial. Nociceptor function was measured by determining the
... infulness of 0.1% topical capsaicin applied to the pre-tibial area of each subject for 30 minutes during screening. Subjects were then randomized to receive 0.1% topical clonidine gel (n=89) or placebo gel (n=90) applied t.i.d. to their feet for 12 weeks. The difference in foot pain at week 12 in relation to baseline, rated on a 0-10 numerical pain rating scale (NPRS), was compared between groups. Baseline NPRS was imputed for missing data for subjects who terminated the study early. The subjects treated with clonidine showed a trend toward decreased foot pain compared to the placebo-treated group (the primary endpoint; p=0.07). In subjects who felt any level of pain to capsaicin, clonidine was superior to placebo (p<0.05). In subjects with a capsaicin pain rating ≥2 (0-10, NPRS), the mean decrease in foot pain was 2.6 for active compared to 1.4 for placebo (p=0.01). Topical clonidine gel significantly reduces the level of foot pain in PDN subjects with functional (and possibly sensitized) nociceptors in the affected skin as revealed by testing with topical capsaicin. Screening for cutaneous nociceptor function may help distinguish candidates for topical therapy for neuropathic pain.